In a large bowl, place the flour, baking powder, sugar, lemon zest, rosemary, blueberries and oats, along with a pinch of salt. Stir well.
Add the butter and mush it all together until the mixture starts to resemble coarse crumbs (you can use your hands for this step).
Beat the egg and milk together, then add to the dry ingredients. Stir well until it all comes together in a wet ball.
Sprinkle a little flour on your work surface, and place the scone ball on it. The dough will be wetish, so carefully pat it out into a circle. Cut the circle in half, then into quarters, then into eighths. Remove each triangle carefully to a parchment-lined baking pan. Brush with additional milk.
Bake in a preheated 400 degree oven for about 20 minutes, or until the scones are toasty on top.
Remove from oven and let cool on the pan slightly, then move to a wire rack to cool completely.
To glaze: Place the icing sugar in a small bowl, and slowly begin adding the lemon juice, a little at a time, until you get the right consistency. you want the glaze to be runny enough that it will drip off of a spoon or the end of your whisk, but not so runny that it's not opaque when it lands on the scone. Drizzle the glaze over the scones and serve.